A variety of automatic tools have been developed over the years for rapidly installing nuts or collars on high-strength aerospace fasteners. Typically these automatic tools are pneumatically operated and can be used rapidly so that the myriad number of fasteners on modern aircraft or the like can be installed with a minimum amount of assembly time.
There are a variety of requirements for such tools. Nuts should be automatically delivered to the tool in a position to be quickly installed on a bolt without manual intervention by the operator. For example, the tools should be useable in any orientation since the fasteners to be assembled may sometimes be overhead or beneath the worker or in front of the worker using the tool. For threaded fasteners, it is often desirable to provide a nonrotating key coaxial with a rotating nut to keep the threaded fastener or "pin" from rotating until the nut is installed.
Naturally, there are certain operating efficiencies which are also desirable. For example, the tools should operate quickly and reliably to provide uniform tightening of nuts on bolts. Preferably the time between installing one nut and having the next nut ready for installation should be minimized. The amount of air usage should be minimized.
Some nuts, such as those in U.S. Pat. No. 4,260,005, have a flange which is assembled against the workpiece being connected by the fastener. The mechanisms for handling such nuts must be designed to accommodate such a flange. The flange geometries may vary with different embodiments of nuts and some adaptability in that regard is therefore desirable in the automatic nut installation tool.
With the special nut mentioned above, the driver for the nut is relatively large and the operating mechanisms must accommodate this size. Such a nut has three outwardly extending lobes on its outer surface which are engaged by a generally triangular or deltoid driver. When the nut has been tightened onto the bolt with a preselected clamp-up force, the driver deforms the lobes radially inwardly so that the external surface of the nut is substantially round. The deformation of the lobes also deforms the inside of the nut for engaging a somewhat nonround thread on the bolt, thereby inhibiting removal of the nut from the bolt. Furthermore, the deformation of the lobes occurs at a preset force so that the clamp-up load installed on the workpiece by the fastener is well known.
Because of the requirement for deforming the lobes on the nut, a strong and abrasion resistant nut driver is required. Typically this is made of cemented tungsten carbide, which tends to be a brittle material subject to breakage in tension. The driver is therefore mounted in a steel backup sleeve to provide the required strength. This results in a driver which is substantially larger than the nut and may also be larger than required for other types of fasteners.
A prior nut installation tool uses a ring-shaped shuttle for delivering a flanged nut in front of a driver. The outside diameter of the driver is the same size as the diameter of the flange on the nuts used with the device. Thus, the driver may pass through the shuttle. When the driver is larger than the flange on the nut, a different type of shuttle must be used where the shuttle moves out of the way of the nut driver.
Another device available from Huck Manufacturing Co. for installing swaged collars has a shuttle which moves out of the way of a collar pick up pin. In that device there is a pin which enters the bore of a collar. Since this is not a portable device and always operates in a vertical orientation, the collar fits loosely on the pin. Furthermore, when the swaged collar is tightened there is no rotation of the collar relative to the nut. Thus, the operating mechanisms are not, in general, suitable for installing threaded fasteners.
In an automatic nut driver as shown in U.S. Pat. No. 3,750,257, which is suitable for threaded fasteners, the entire pneumatic cylinder rotates, a situation which is undesirable because of opportunities for leakage.
It is also desirable to use a standard pneumatic wrenching tool for the automatic nut installation tool rather than manufacturing new pneumatic components. This appreciably diminishes the cost of the nut installation tool, since the pneumatic motor, gearbox and the like, need not be specially manufactured. By simply mounting the entire apparatus on a standard pneumatic wrench, one can also provide for easy replacement and repair of the components, as may be required from time to time.